Hydraulic circuit for the control of forward and reverse shift clutches

Abstract

A hydraulic load power train control for reversible shifting with a pressure control device for the controlled build-up of a shift clutch pressure, a foot clutch valve for arbitrary control of the shift clutches, and a manually operable shift valve for shifting of the reversible power train. The foot clutch valve is connected parallel to the pressure control device. The pressure control device is formed by a changeover valve indirectly reversible by the shift valve by which the pressure controlled in the supply pressure line can be fed to two shift pressure lines which are connected to a valve device. At the same time, the valve device is so controlled by the foot clutch valve that the effective shift clutch pressure can be controlled without influencing the position of the changeover valve as a function of the actuation of the foot clutch. The hydraulic load power train control, on the one hand, makes possible, in the case of engaging or reversing of the shift clutches, a smooth transition from one gear to the other and, at the same time, a delay-free start in the shifting by actuation of the foot clutch.

What is claimed as new desired to be secured by Letters Patent of the United States is: 
     
       1. A hydraulic circuit for the control of forward and reverse shift clutches, said hydraulic circuit comprising: (a) a pressure control device for the controlled build-up of a shift clutch pressure, said shift clutch pressure being for use to actuate either a forward shift clutch or a reverse shift clutch;   (b) a foot clutch valve operatively connected to each of the shift clutches via a respective inverted shuttle valve; and   (c) a manually operable shift valve for clutch or said reverse clutch,   wherein:   (d) said foot clutch valve is connected in parallel to said pressure control device;   (e) said pressure control device comprises a changeover valve that has a neutral position, a position in which shift clutch pressure is connected to said forward shift clutch, and a position in which shift clutch pressure is connected to said reverse shift clutch and that can be shifted to any one of its positions by said manually operable shift valve via two shift control lines;   (f) said changeover valve feeds the pressure in a supply pressure line to one or the other or to both of two shift pressure lines, one of which leads to said forward shift clutch and one of which leads to said reverse shift clutch;   (g) each of said two shift pressure lines is connected to a respective one of said inverted shuttle valves, each one of said inverted shuttle valves being controlled by said foot clutch valve;   (h) a pressure reducing valve is connected upstream of said changeover valve; and   (i) each one of said inverted shuttle valves having two inputs and one output, a first input connection of each one of said pair of inverted shuttle valves being connected to a control line of said foot clutch valve, a second input connection of each one of said pair of inverted shuttle valves being connected to a respective one of said two shift pressure lines, and the output connection of one of said pair of inverted shuttle valves being connected to said forward shift clutch and the output connection of the other one of said pair of inverted shuttle valves being connected to said reverse shift clutch.   
     
     
       2. A hydraulic circuit according to claim 1 wherein said changeover vale is a three-way valve prestressed in a throttle interconnection position (B), said three-way valve comprising a piston slide having opposing control front surfaces which, in each case, are acted on by a feed back control line branching off from one of said shift pressure lines, said feed back control lines being in each case in fluidic communication by a shift control line with said manually operable shift valve for opening and closing, respectively, said shift control lines. 
     
     
       3. A hydraulic circuit according to claim 2 wherein a throttle is incorporated in each of said feed back control lines. 
     
     
       4. A hydraulic circuit according to claim 1 wherein said shift valve is a three-way valve prestressed in its center position (B), in which it discharges said shift control lines, said shift valve having a piston slide that can be manually moved into a shift position (A) in which one of said shift control lines is discharged and into a shift position (C) in which the other one of said shift control lines is discharged. 
     
     
       5. A hydraulic circuit according to claim 4 wherein said piston slide of said shift valve has two notched recesses, each one of which can be brought to engage a stop piston, with which said shift valve can be locked in its two shift positions (A and C). 
     
     
       6. A hydraulic circuit according to claim 5 wherein: (a) said stop piston is received in a working cylinder;   (b) said stop piston limits a pressure chamber in said working cylinder; and   (c) said pressure chamber is connected to a hydraulic pressure circuit.   
     
     
       7. A hydraulic circuit according to claim 6 wherein said pressure chamber of said stop piston is connected to an oil hydraulic circuit. 
     
     
       8. A hydraulic circuit according to claim 4 wherein said shift control liens can be discharged into an oil hydraulic circuit. 
     
     
       9. A hydraulic circuit according to claim 1 wherein said foot clutch valve is a three-way valve, which in its Clutch engaged condition (A) connects said control line of said foot clutch valve with pressure (p 1 ) in said supply pressure line and in its clutch disengaged position (C) connects said control line of said foot clutch valve to a pressure discharge. 
     
     
       10. A hydraulic circuit according to claim 9 wherein the discharge of said control line of said foot clutch valve takes place in an oil hydraulic circuit. 
     
     
       11. A hydraulic circuit according to claim 10 wherein the pressure in said oil hydraulic circuit is less than 2 bars. 
     
     
       12. A hydraulic circuit according to claim 1 wherein said pressure reducing valve is sized, shaped, and positioned to reduce supply pressure (p 1 ) by about 3 bars. 
     
     
       13. A hydraulic circuit according to claim 12 wherein supply pressure (p 1 ) is about 15 bars.